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Who needs ‘lazy’ workers? Inactive workers act as a ‘reserve’ labor force replacing active workers, but inactive workers are not replaced when they are removed

1 , * , 2 , 3

PLoS ONE

Public Library of Science

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      Abstract

      Social insect colonies are highly successful, self-organized complex systems. Surprisingly however, most social insect colonies contain large numbers of highly inactive workers. Although this may seem inefficient, it may be that inactive workers actually contribute to colony function. Indeed, the most commonly proposed explanation for inactive workers is that they form a ‘reserve’ labor force that becomes active when needed, thus helping mitigate the effects of colony workload fluctuations or worker loss. Thus, it may be that inactive workers facilitate colony flexibility and resilience. However, this idea has not been empirically confirmed. Here we test whether colonies of Temnothorax rugatulus ants replace highly active (spending large proportions of time on specific tasks) or highly inactive (spending large proportions of time completely immobile) workers when they are experimentally removed. We show that colonies maintained pre-removal activity levels even after active workers were removed, and that previously inactive workers became active subsequent to the removal of active workers. Conversely, when inactive workers were removed, inactivity levels decreased and remained lower post-removal. Thus, colonies seem to have mechanisms for maintaining a certain number of active workers, but not a set number of inactive workers. The rapid replacement (within 1 week) of active workers suggests that the tasks they perform, mainly foraging and brood care, are necessary for colony function on short timescales. Conversely, the lack of replacement of inactive workers even 2 weeks after their removal suggests that any potential functions they have, including being a ‘reserve’, are less important, or auxiliary, and do not need immediate recovery. Thus, inactive workers act as a reserve labor force and may still play a role as food stores for the colony, but a role in facilitating colony-wide communication is unlikely. Our results are consistent with the often cited, but never yet empirically supported hypothesis that inactive workers act as a pool of ‘reserve’ labor that may allow colonies to quickly take advantage of novel resources and to mitigate worker loss.

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      The large-scale organization of metabolic networks

      In a cell or microorganism the processes that generate mass, energy, information transfer, and cell fate specification are seamlessly integrated through a complex network of various cellular constituents and reactions. However, despite the key role these networks play in sustaining various cellular functions, their large-scale structure is essentially unknown. Here we present the first systematic comparative mathematical analysis of the metabolic networks of 43 organisms representing all three domains of life. We show that, despite significant variances in their individual constituents and pathways, these metabolic networks display the same topologic scaling properties demonstrating striking similarities to the inherent organization of complex non-biological systems. This suggests that the metabolic organization is not only identical for all living organisms, but complies with the design principles of robust and error-tolerant scale-free networks, and may represent a common blueprint for the large-scale organization of interactions among all cellular constituents.
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        Regulation of division of labor in insect societies.

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          Models of division of labor in social insects.

          Division of labor is one of the most basic and widely studied aspects of colony behavior in social insects. Studies of division of labor are concerned with the integration of individual worker behavior into colony level task organization and with the question of how regulation of division of labor may contribute to colony efficiency. Here we describe and critique the current models concerned with the proximate causes of division of labor in social insects. The models have identified various proximate mechanisms to explain division of labor, based on both internal and external factors. On the basis of these factors, we suggest a classification of the models. We first describe the different types of models and then review the empirical evidence supporting them. The models to date may be considered preliminary and exploratory; they have advanced our understanding by suggesting possible mechanisms for division of labor and by revealing how individual and colony-level behavior may be related. They suggest specific hypotheses that can be tested by experiment and so may lead to the development of more powerful and integrative explanatory models.
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            Author and article information

            Affiliations
            [1 ] Graduate Interdisciplinary Program in Entomology & Insect Science, University of Arizona, Biological Sciences West, 1041 East Lowell, Tucson, AZ, United States of America
            [2 ] Department of Zoology, University of Oxford, Oxford, United Kingdom
            [3 ] Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, United States of America
            University of Sheffield, UNITED KINGDOM
            Author notes

            Competing Interests: The authors have declared that no competing interests exist.

            Contributors
            ORCID: http://orcid.org/0000-0002-9537-4763, Role: Conceptualization, Role: Data curation, Role: Formal analysis, Role: Investigation, Role: Methodology, Role: Project administration, Role: Writing – original draft, Role: Writing – review & editing
            Role: Conceptualization, Role: Methodology, Role: Writing – review & editing
            Role: Conceptualization, Role: Formal analysis, Role: Investigation, Role: Methodology, Role: Supervision, Role: Writing – original draft, Role: Writing – review & editing
            Role: Editor
            Journal
            PLoS One
            PLoS ONE
            plos
            plosone
            PLoS ONE
            Public Library of Science (San Francisco, CA USA )
            1932-6203
            6 September 2017
            2017
            : 12
            : 9
            28877229
            5587300
            10.1371/journal.pone.0184074
            PONE-D-16-35177
            (Editor)
            © 2017 Charbonneau et al

            This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

            Counts
            Figures: 5, Tables: 1, Pages: 20
            Product
            Funding
            Funded by: funder-id http://dx.doi.org/10.13039/100000154, Division of Integrative Organismal Systems;
            Award ID: IOS-1045239
            Award Recipient :
            Funded by: funder-id http://dx.doi.org/10.13039/100000154, Division of Integrative Organismal Systems;
            Award ID: IOS-0841756
            Award Recipient :
            Funded by: funder-id http://dx.doi.org/10.13039/100000153, Division of Biological Infrastructure;
            Award ID: DBI-1262292
            Award Recipient :
            Research supported through the GIDP-EIS and EEB Department at University of Arizona, as well as NSF grants no. IOS-1045239, IOS-0841756, and DBI-1262292 (to A.D.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
            Categories
            Research Article
            Biology and Life Sciences
            Organisms
            Animals
            Invertebrates
            Arthropoda
            Insects
            Biology and Life Sciences
            Organisms
            Animals
            Invertebrates
            Arthropoda
            Insects
            Hymenoptera
            Ants
            Biology and Life Sciences
            Organisms
            Animals
            Invertebrates
            Arthropoda
            Insects
            Hymenoptera
            Bees
            Honey Bees
            Biology and Life Sciences
            Behavior
            Animal Behavior
            Foraging
            Biology and Life Sciences
            Zoology
            Animal Behavior
            Foraging
            Computer and Information Sciences
            Systems Science
            Complex Systems
            Physical Sciences
            Mathematics
            Systems Science
            Complex Systems
            Computer and Information Sciences
            Computer Networks
            Biology and Life Sciences
            Genetics
            Gene Identification and Analysis
            Genetic Networks
            Computer and Information Sciences
            Network Analysis
            Genetic Networks
            Biology and Life Sciences
            Physiology
            Physiological Processes
            Food Consumption
            Medicine and Health Sciences
            Physiology
            Physiological Processes
            Food Consumption
            Custom metadata
            All data files are available from the Dryad database (Provisional DOI: doi: 10.5061/dryad.77110).

            Uncategorized

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